Objective: This prospective study reports on the prevalence of hearing impairment in an at-risk neonatal intensive care unit (NICU) population.
Design: From 1990 to 1998, 1062 neonates were screened with the use of transitory evoked otoacoustic emissions (TEOAE) and brainstem evoked response audiometry (BERA).
Results: 934 infants passed the primary screen for both ears, 75 for one ear, adding up to 95%. 17 infants (1.6%) were lost to follow-up. In fourteen infants (1.3%), bilateral hearing impairment above 30 dB was confirmed. While all children with hearing impairment belonged to the group of 862 children receiving aminoglycosides, only one of them presented no other risk factors. In twelve of the hearing impaired children other anamnestic factors, i.e. dysmorphism, prenatal rubella or cytomegaly, family history of hearing loss or severe peri- and postnatal complications seem to be more probable causes of the identified hearing loss. In one of these children, delayed onset or progression of hearing loss is suspected.
Conclusions: From our data, aminoglycosides are not an important risk factor for hearing impairment, when serum levels are continuously monitored, as in our cohort. After adjustment for other risk factors, birth weight between 1000 gr and 1500 gr and a gestational age between 29 and 31 weeks were no predictive markers for hearing impairment. It might be speculated that the improved medical treatment in a NICU reduces the probability of hearing impairment for those two groups. Conductive hearing loss as a possible additional cause for hearing impairment was not studied in detail, but the high percentage of malformations detected (four out of fourteen hearing impaired infants) demands further monitoring, close follow-up, adequate treatment and counselling.